Radar Sea Return in High Sea States

摘要

In order to obtain a more exact specification of the variation of the radar cross section of the sea with increasing sea roughness, and to determine a worst-case condition for sea clutter, a high-sea-state clutter measurement program in the North Atlantic was conducted. Radar return was collected on four frequencies in both linear and cross polarizations, and the normalized radar section sigma sub o of the sea surface was obtained as a function of radar and surface parameters for the high sea states encountered. The study of the behavior of the median value of sigma sub o as a function of the radar parameters and sea conditions resulted in the following conclusions at high sea states characterized by winds of 20-50 knots and wave heights of 10-26 ft: (a) the value of sigma sub o is independent of wavelength for vertical polarization but maintains an inverse wavelength dependence for horizontal polarization, (b) the direct polarization ratio remains significnt for all wavelengths as the sea roughness increases and is a function of wavelength, (c) the value of sigma sub o is sensitive to wind direction, with consistently higher clutter observed in the upwind direction for all wavelengths and both direct polarizations, and (d) the value of sigma sub o does not increase significantly with wind velocity in the region 20-50 knots, indicating that sigma sub o approaches a maximum value, or 'saturation,' with increasing surface roughness. (Author)